In processing of silver halide color photographic materials, spent processing solutions are generally discarded as an overflow. However, recovered and disposed spent processing solutions cause great environmental pollution and are unfavorable for environmental conservation. Also, the cost incurred for the recovery is not negligible. If these spent processing solutions (overflows) could be reused as a replenisher, it would offer a solution to the environmental and economic problem. In addition, since active components remaining in the overflow could be utilized, the amounts of chemicals necessary for preparing a replenisher would be significantly reduced as compared with preparing a fresh replenisher to thereby further reduce the cost. Extensive studies have been directed to regeneration of spent processing solutions to make them reusable by correcting the changes brought about during processing, generally by removal of accumulated components which adversely affect photographic properties and replacing the consumed components.
With respect to a bleach-fix bath used for processing color photographic materials, various efforts have also been made to develop techniques of regeneration.
A bleach-fix bath generally contains chemicals for at least three functions, i.e., an aminopolycarboxylic acid iron (III) complex serving as a bleaching agent, a thiosulfate serving as a fixing agent, and a sulfite serving as a preservative. An overflow of the bleach-fix bath additionally contains silver ion produced by desilvering action and color developer components which have been carried over from the prebath. The overflow further contains an iron (II) aminopolycarboxylate resulting from oxidation of silver to silver ions.
As described above, regeneration of a processing solution generally requires removal of harmful accumulated components and addition of consumed components, and how to effectively remove the accumulated components has been a problem waiting for a solution. In order to solve this problem, various regeneration systems for removing or reducing silver ions resulting from desilvering have been proposed.
A regeneration method in which a spent bleach-fix bath is contacted with metallic iron (steel wool) is disclosed in Radiography, Vol. 29, pp. 256-259 (1963) and JP-A-48-3624 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). According to this method, while silver ions contacted with metallic iron are recovered as metallic silver to reduce the silver ion concentration, metallic iron is dissolved into a bleach-fix bath as a strongly reducing iron (II) ion to weaken the oxidizing ability of the bath. As regeneration is repeated, metallic iron is dissolved to greatly vary the iron ion concentration, making it difficult to stably control the concentration. As the silver ion concentration is reduced, this problem becomes pronounced.
A method for reducing silver ions by electrolysis is described in JP-B-53-40491 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A-51-19535 (West German Patent 2534920), JP-A-51-36136, and U.S. Pat. No. 4,014,764. In this case, too, an iron (III) complex is reduced to an iron (II) complex or a sulfite ion is oxidized to a sulfate ion at the anode, which seriously fatigues the processing solution and, at the same time, reduces stability of the solution. This problem becomes more pronounced as the amount of electricity is increased to raise the rate of silver recovery and to reduce the silver ion concentration in the bleach-fix bath.
A technique for removing a silver complex by adsorption onto an ion exchange resin is proposed in J. Appl. Photogr. Eng., Vol. 6, pp. 14-18 (1980). However, this method involves complicated operations for releasing an adsorbed silver complex from the resin to regenerate the resin. Besides, it produces a large quantity of a waste liquid and is unsatisfactory from the standpoint of running cost.
Thus, the conventional techniques for removing or reducing unnecessary components from a spent processing solution to make the solution reusable generally encounter difficulty in controlling the final ratio of the components or analyzing the components, involve complicated operations, and require large-sized equipment for regeneration.
JP-B-56-33697 (British Patent 1405948) and JP-A-50-145231 disclose a technique for regenerating an overflow, in which silver is not positively removed, but, when necessary, an equilibrium amount of accumulated silver ion is relatively reduced, for example, by dilution. This method is simple, easy, and inexpensive to carry out and requires no special equipment for silver recovery.
However, this method, when used alone, has causes delay in desilvering due to accumulation of silver bromide dissolved out in a large quantity and accumulation of a sulfate. Eventually, this method tends to cause undesirable stain due to accumulation of developer components or poor color reproduction, resulting from poor stability of running performance. When this method is utilized, particularly for reuse of a bleach-fix bath, halide ions accumulate and silver ions, an iron (II) aminopolycarboxylate accumulate and, in addition, developer components or a sulfate resulting from oxidation of a sulfite ion accumulates. It appears that these accumulated components act on each other in a complex fashion or act as a whole, and result in delay in desilvering, formation of a leuco cyan dye (which leads to poor color reproduction), deterioration of image preservability, and particularly thermal discoloration of a cyan dye. Such a phenomenon becomes more pronounced in rapid processing.
Therefore, development of a technique for regenerating an overflow generally is difficult and, above all, regeneration of a bleach-fix bath is very difficult because of the complicated action of the components contained or accumulated.
It has been suggested that addition of a water-soluble compound having an aldehyde group or a methylol group to a bleach-fix stabilizing bath makes rapid processing feasible and prevents yellow staining (which is believed ascribed chiefly to the action of formalin) as disclosed in JP-A-48-42733. Further, JP-A-50-51326 (U.S. Pat. No. 4,033,771) and JP-A-56-107244 (U.S. Pat. No. 4,033,771) describe that addition of a carbonyl bisulfite addition compound to a bleach-fix bath retards sulfiding of the bleach-fix bath and also prevents formation of a leuco cyan dye. However, in a regenerated system in which a spent bleach-fix bath is repeatedly reused, the influences of various accumulated components, are greater than expected as mentioned above, so that conventioned regeneration techniques for a bleach-fix bath cannot be simply applied. Moreover, the above-described conventional techniques do not solve the problems arising in the regeneration of a bleach-fix bath, such as delay in desilvering and deterioration of image preservability (particularly thermal discoloration of a cyan image).